Fluid coolant under pressure is typically supplied to the cutting tool of a machine tool while it is machining a workpiece for lubricating and cooling the cutting tool, as well as flushing chips of workpiece material from it and out of its path of travel, to increase machining efficiency and prolong the life of the cutting tool by preventing excessive chip buildup on the tool. Typically, the cutting tool has one or more coolant passages within it that each lead to an opening or coolant orifice for enabling coolant to be delivered to a cutting surface of the tool while it is engaged with the workpiece during machining. Coolant delivery systems that supply coolant to a cutting tool are usually classified as either low pressure or high pressure coolant delivery systems depending upon the pressure of coolant supplied to the tool. In assembly line applications, these systems are usually designed to deliver coolant to several cutting tools, typically as many as twenty, forty, sixty or more cutting tools.
For high speed rotary machining applications, such as milling, drilling, boring, reaming and tapping, a higher volume of coolant under a considerable amount of pressure must be provided at the cutting surface of the cutting tool as it is engaging the workpiece during machining for providing lubrication at points of contact between the tool and workpiece while also cooling the cutting tool. A large volume of coolant under high pressure is also needed to free the cutting tool of excessive chip buildup and flush chips of workpiece material out of its path of travel for preventing excessive loading of the tool during machining which can undesirably lead to premature failure of the cutting tool.
Unfortunately, excessive chip buildup can occur on the cutting tool even while high pressure coolant is being supplied. Excessive chip buildup on the cutting tool can obstruct coolant flow to the cutting tool and cause the tool to prematurely fail or, even worse, result in workpieces that are defectively machined. Additionally, reduced coolant flow to the cutting surfaces of the tool reduces lubrication between the cutting tool and workpiece thereby reducing machining efficiency and possibly decreasing machining quality. As such, obstructed coolant passages and premature cutting tool failure reduce machining efficiency, lower production rates and thereby increase machining costs.
At other times of high speed rotary cutting tool operation other than machining, at least some coolant flow to the cutting tool is required for simply cooling the tool. Additionally, many of these machine tools require coolant to cool and lubricate a rotating coolant coupling of the machine tool, called a rotary union, during those periods of operation when high pressure coolant is not being supplied to the cutting tool.
However, virtually all high pressure systems continuously operate a pump to supply coolant under high pressure to the cutting tool at all times, even when the cutting tool is not engaging the workpiece, such as when workpieces are being transferred into and out of the machine tool station, while the cutting tool is approaching the workpiece to machine it, and while the tool is being retracted from the workpiece after machining it. Other coolant delivery systems also have a source of lower pressure coolant and use separate coolant circuits for delivering coolant to those cutting tools requiring high pressure coolant and those cutting tools requiring lower pressure coolant. In these high-low pressure coolant delivery systems, a high pressure pump also continuously operates to supply coolant under high pressure to those high speed cutting tools that require high pressure coolant. A second low pressure pump continuously supplies coolant at a lower pressure to any machine tool, such as a broaching machine, which does not require high pressure coolant flow.
Similarly, at workpiece flushing stations requiring a high pressure stream of a fluid, typically coolant, directed through an orifice into a deep hole in a workpiece for cleaning it of chips and debris, the pump used to supply the fluid is a conventional rotary high pressure pump powered by an electric motor that runs continuously. Since the pump is running continuously, to stop coolant flow to the workpiece, such as when transferring the workpiece out of the station and while receiving another workpiece into the station, a fluid switching valve directs coolant back to a coolant supply or reservoir.
Typically, the high pressure pump operates continuously to avoid excessive pump wear and premature failure that undesirably would occur if the pump were cycled to supply high pressure coolant to the cutting tool only when needed. Therefore, many of these high-low pressure coolant delivery systems supply high pressure coolant continuously to cutting tools requiring it, both while the tool is machining the workpiece and when it is not in contact with any workpiece. As a result, continuous high pressure pump operation consumes excessive electrical power and reduces the life of filters required to remove sediment from the coolant before it reaches the cutting tool.
However, even if the high pressure pump could be economically cycled to provide high pressure coolant only when needed, some lesser flow of coolant must be supplied to rotary machine tools when the high pressure pump is not supplying coolant to the tool for cooling and lubricating the bearings of the rotary union as well as, preferably, cooling the tool. Variable pressure coolant pumps capable of providing both high and low pressure coolant flow from a single pump are not known and would likely be undesirably expensive and/or less reliable.
Other, simpler, coolant delivery systems use a pump that intermittently forces a coolant or lubricant to the cutting tool or other moving parts of the machine tool to lubricate them. Representative of these coolant and lubricant delivery systems are U.S. Patents: Mirrielees U.S. Pat. No. 1,398,338; Bennett U.S. Pat. No. 2,190,858; Bonnafe U.S. Pat. No. 2,333,147; and Shaffer U.S. Pat. No. 4,597,697. However, none of these systems supply coolant to the cutting tool at high pressure while machining the workpiece and low pressure during other times of machine tool operation. Furthermore, none of these systems sense coolant flow to the cutting tool for determining when there is an obstruction of a coolant passage or orifice of the cutting tool or tool failure.